Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 03-09-2007, 20:29   #1
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Tasmania
Boat: VandeStadt IOR 40' - Insatiable
Posts: 2,317
Images: 91
Genoa cars - sizing?

I am in the process of replacing the old genoa cars on my boat.

Using formulas in the Harken catalogue, the sail areas for my boat’s various sails and the manufacturer's quoted (a) safe working loads and (b) minimum breaking loads for the proposed genoa cars, It is possible to calculate the wind speeds, for each sail, that would be necessary in order to reach both the safe working load and minimum breaking load

Assuming that I have done the math correctly, then

The wind speeds at which the load on the genoa car reaches the manufacturer’s Safe Working Load are as follows:

#1 34.4 knots
#2 37.4 knots
#3 43.8 knots
#4 52.4 knots
Storm jib 78.8 knots

The wind speeds at which the load on the genoa car reaches the manufacturer’s Minimum Breaking Load are as follows

#1 48.7 knots
#2 52.9 knots
#3 64.0 knots
#4 76.5 knots
Storm jib 115 knots

Do these figures, in your opinion, indicate that my proposed choice of genoa cars are suitable?

__________________

__________________
Weyalan is offline   Reply With Quote
Old 03-09-2007, 21:10   #2
Registered User

Join Date: May 2007
Location: Currently East Coast USA/Caribbean
Boat: Stevens 47
Posts: 223
Images: 2
You can verify your calculations on the Harken website "Genoa Sheet Loading" Calculator Conversion Calculator-Geanoa Loading.
__________________

__________________
svTOTEM is offline   Reply With Quote
Old 03-09-2007, 21:41   #3
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Tasmania
Boat: VandeStadt IOR 40' - Insatiable
Posts: 2,317
Images: 91
Thanks for the link. I am actually reasonably confident in my math. I am interested to hear whether people think that the wind speeds to reach the SWL and MBL indicate an appropriate choice of genoa car....
__________________
Weyalan is offline   Reply With Quote
Old 04-09-2007, 10:44   #4
Registered User

Join Date: May 2007
Location: Currently East Coast USA/Caribbean
Boat: Stevens 47
Posts: 223
Images: 2
No, I would say that you've spec'd a genoa car that is a size to big. Without actually seeing your boat, but having sailed/raced on many IOR boats, I think a top (designed) wind range for each headsail is something like:
#1 16 knots
#2 24 knots
#3 34 knots
#4 42 knots
Storm jib, likely you go to bare poles in the 60ish knot range

In my view there are other variables to consider. What is the sailcloth that each sail is made from? Any sort of high modulus material (Spectra, Dyneema, Kevlar, etc) will significantly increase the sheet loads (no stretch means quicker and more efficient transfer of energy from wind gust to sail to boat). Similarly, what are the sheets and halyards made from? When the wind pipes up toward the top of its range, do you reduce the size of the headsail or say wahoo this is fun?

If you’re racing, then weight is always an issue. If you’re cruising it makes sense to be conservative with safe working loads, but within practical limits.
__________________
svTOTEM is offline   Reply With Quote
Old 04-09-2007, 15:39   #5
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Tasmania
Boat: VandeStadt IOR 40' - Insatiable
Posts: 2,317
Images: 91
Thanks for the feedback. I appreciate it. The boat is a standard early 80's design 40' "1-tonner", although slightly more of a cruiser-racer layout than some of the stripped out racing machines. I do race it regularly, although that is not it's main raison d'etre.

You are probably right; I probably have over-specced slightly, but I would rather be slightly over-specced than under!

In fact, the exercise is reasonably academic because I have already purchased the genoa cars (on eBay, brand new, for about 20-25% of the RRP!).

Thanks again.
__________________
Weyalan is offline   Reply With Quote
Old 04-09-2007, 15:59   #6
Registered User

Join Date: May 2007
Location: Currently East Coast USA/Caribbean
Boat: Stevens 47
Posts: 223
Images: 2
I'm always happy when I can pay less and get more.
__________________
svTOTEM is offline   Reply With Quote
Old 04-09-2007, 16:43   #7
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Tasmania
Boat: VandeStadt IOR 40' - Insatiable
Posts: 2,317
Images: 91
Just out of interest, with a standard IOR rig (i.e. 3/4 frac, running backstays, checkstays, etc) assuming the mainsail has 2 largish reefs, at what wind speed would you put in reef 1 and at what speed reef 2?
__________________
Weyalan is offline   Reply With Quote
Old 04-09-2007, 19:12   #8
Registered User

Join Date: May 2007
Location: Currently East Coast USA/Caribbean
Boat: Stevens 47
Posts: 223
Images: 2
That very question came to mind when posting earlier. I started writing about that as one of the "variables" with sheet load and then it got a little complicated so I dropped it. Here goes my best short answer. From a racing perspective there were 2 approaches to managing the sail combinations, on an IOR design boat.

Being that yours is fractional your approach is likely: at about 20 kts you would go from a heavy #1 (meaning flatter, 147%ish overlap) to a #3 and keep the full main (traveler down with twist). The 20 kt number is give or take depending on the sea state; bigger/choppy sea require more power vs flat sea less power. I think you take the first reef in the 28 to 30 kt range. Then you would go to a #4 in the upper 30's. Finally a 2nd reef goes in beyond that.

Older IOR boats with a shorter E (mainsail foot length) would reef first, then go to a #3, then a second reef, then a #4. It has to do the efficeincy of balance vs power. If I'm right about your boat, then you will be able to maintan the most sail area with relatively less adverse affect from weather helm, leeway etc. It is important that you play the main traveler a lot, and sheet to a lesser extent, as you approach the top of the range for a given sail combination. Go out on a breezy day and reduce sail the scenarios stated above, making notes of speed and heading before and after each change.

Now, from a cruising perspective you reef the main when your wife tells you to.
__________________
svTOTEM is offline   Reply With Quote
Old 04-09-2007, 19:50   #9
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Tasmania
Boat: VandeStadt IOR 40' - Insatiable
Posts: 2,317
Images: 91
I really appreciate your taking the time to type out all this information; so thanks very much. While I do have a few years of experience crewing on other people's boats (including another IOR 40' 1-tonner), I have only owned my boat for about 20 months, and on other people's boats, you tend to change sails / reef when the owner/skipper/tachtician tells you, but on your own boat you tend to have to make those decisions for yourself.

From the racing point of view I do prefer the fractional IOR rig to the masthead (I don't like those monster #1 headsails and relatively small main), although since short-handed cruising is the boat's main use, running backstays are a pain in the butt.

For what it is worth, on my boat, P is about 50' and E about 18', so a reasonable sized main for an IOR boat.

Fully crewed, racing round the cans, we will carry the #1 to just about 18 knots, then the #2 to around 25, and when it gets over about 35 they generally cancel the race, so we don't often see the #4. Offshore (I don't race much offshore), we are more conservative. Cruising I tend to go with #2 even in light breeze and reef at 20 because usually we are only 2 or perhaps 3 on board and whats the hurry?

For what it is worth I just did the calcs for mainsheet load (using the E & P above). In theory, the load gets very ugly very fast, i.e. Load (kg) = 9.9 x V^2 where V = wind speed in knots.... plug in something like 25knots and it looks like an awfully big load until you consider what you would actually be doing with your main in 25 knots and how much of that main would actually be presented to the wind...

As you can tell, if I can't actually be out sailing, I like to at least think about sailing! 8)
__________________
Weyalan is offline   Reply With Quote
Old 04-09-2007, 21:12   #10
Registered User

Join Date: May 2007
Location: Currently East Coast USA/Caribbean
Boat: Stevens 47
Posts: 223
Images: 2
Sounds like you've got a good handle on what works for your boat.

Same with me. My brain is always on the water even when the body is not. More so know as my wife and I are 9 months from leaving with our 3 kids to go cruising for some years. So much to do. Perhaps we'll make it to your corner of the planet...
__________________
svTOTEM is offline   Reply With Quote
Old 04-09-2007, 22:23   #11
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Tasmania
Boat: VandeStadt IOR 40' - Insatiable
Posts: 2,317
Images: 91
That sounds great. I am jealous. My partner and I are still probably about 5-6 years away from leaving to go cruising for some years and the boat will probably take that long to get up to scratch anyway! If you do happen to make it to our obscure corner of the planet, be sure to send me a PM here and I'll buy you a beer or 3.
__________________
Weyalan is offline   Reply With Quote
Old 05-09-2007, 10:11   #12
Registered User

Join Date: May 2007
Location: Currently East Coast USA/Caribbean
Boat: Stevens 47
Posts: 223
Images: 2
That's reason enough to make it there.
__________________

__________________
svTOTEM is offline   Reply With Quote
Reply

Tags
Genoa

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Sizing a genoa winch IMustBeASailor Deck hardware: Rigging, Sails & Hoisting 21 11-02-2007 18:07
Mainsail batten cars R&B Construction, Maintenance & Refit 9 15-11-2006 00:20
FAST BIKES, V8 CARS AND SLOW BOATS?? Bob Norson Off Topic Forum 68 08-09-2006 17:19
Genoa Cars timjf Deck hardware: Rigging, Sails & Hoisting 9 03-09-2006 16:27
Ammeter Sizing svcattales Electrical: Batteries, Generators & Solar 7 01-09-2005 03:50



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 18:01.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.